1. Field of the Invention
Virtually since the first vertical mill became actively used, operators have displayed a remarkable proclivity for hurting themselves and others by leaving a wrench over the top of the drawbar used in such machines.
The drawbar, with one end protruding above a bearing cap, passes down through the machine where it engages a tapered collet which holds the working tool. In order to change tools, the drawbar is rotated to free the collet and then tapped on the top to break the surface tension and free the tool within the collet. The first operation is typically done with a closed end, box end, wrench, or socket wrench, and then a hammer or other implement is used to tap down the drawbar. Previous methods have a myriad of faults, as well as dangers, the most common of which is the leaving of the wrench engaged with the drawbar when the mill is started. In a typical installation, the length of the wrench exceeds the distance between the center of the drawbar and an adjacent motor and as the motor is started, the drawbar rotates, whipping the wrench around against the side of the motor housing with a possible resultant damage to the drawbar, but with the more likely result of the wrench flying off at high speed and with considerable force, to the obvious detriment of anything or anyone which is in its way. The problem is amplified somewhat by the constant pounding of the top of the drawbar with some hammer or mallet-type instrument. An eventual deformation results and that deformation causes a misfit between the wrench and the drawbar. That misfit makes it even easier for the wrench to fly off if the machine is inadvertently started, but may also result in a rounding of the edges of the typically hexagonal or octagonal shaped drawbar end, meaning an eventual costly replacement. If anything is left on the drawbar when the machine is started, tremendous centrifugal forces will be imparted to it and if it flies off under any circumstances, it becomes exceeedingly dangerous.
The present invention provides the operator of such a machine with a specially designed and highly innovative tool which serves both as a socket wrench and as a mallet for tapping the top of the drawbar. As will be described in detail, the tool is so designed as to greatly decrease the danger to persons and property around the machine if the tool is inadvertently left in mating engagement with the drawbar. It is also designed to greatly inhibit any downward movement of the drawbar with the tool in place on the exposed end thereof, thereby minimizing the danger of the tool flying off under such circumstances.
The invention in a further aspect provides a remote tool holder which may be sensitized to actuate a power cut off switch whereby the machine is rendered inoperative except when the tool is in its proper place, i.e., the tool holder, during operation of the machine. This aspect of the invention contemplates the use of a tool operated switch disposed between a power source and the mill motor which, in its normally open position, deprives the machine tool of power. When the tool is placed in a remote holder, however, the switch is automatically closed permitting the machine to be operated. This facet of the invention insures that the operator of the machine has removed the tool and properly stored it before the machine can be operated.
2. Description of the Prior Art
Until the advent of the present invention, operators of the machines of this type have typically used two tools, namely a wrench for rotating the drawbar and a mallet for tapping it to free the collet. There does exist a combination wrench-hammer currently sold by SPI in which a standard mallet construction includes a socket wrench on the hammer head opposite the striking surface. That device has none of the unique features of the present invention.